Method of vulcanizing rubber and resulting products



Patented Nov. 5, 1929 UNITED STATES PATENT OFFICE HENRY B. MORSE, OF DANVERS, MASSACI-TUSETTS, ASSIGNOR, BY MESN E ASSIGNMENTS. TO ALBERT C. BURRAGE, JR., 0]? IPSWICH, MASSACHUSETTS METHOD OF VULCANIZING RUBBER AND RESULTING IRODUCTS No Drawing.

This invention relates to the art of treating rubber or rubber compounds, and has for an object the provision of an improved procedure for the vulcanization of the same in the presence of an accelerator and of compounds or compositions with which to effect the purpose of the invention.

In the art of rubber manufacture, it has long been known that the vulcanizing process may be accelerated by the addition of vaeffect at atmospheric temperature or during.

milling operations, but which actively accelerate the reaction in the customary vulcanizing treatment. Other accelerator compounds, frequently termed ultra accelerators, or semi-ultra accelerators, initiate the vulcanizing reaction sometimes prematurely, either in the cold only or during the mixing operation, resulting in scorching which hinders or entirely prohibits the further use of the rubber or rubber compound. Consequently, such compounds ordinarily have not been used in the manufacture of rubber products, even though they would greatly reduce the time required for vulcanization and may be otherwise suitable for use in rubber compositions.

By the present invention it is found that the accelerating action of accelerator compounds generally in rubber compositions, may be inhibited (at ordinary and slightly elevated temperatures and during the mixing and milling operations) or retarded by the addition of organic compounds of a certain type hereinafter defined, and that thereafter thevulcanizing reaction,ettectively accelerated by the accelerator,may be caused to Application filed June 4 1929. Serial No. 368,428.

proceed at will by subjecting the rubber composition to be vulcanized to vulcanizing conditions.

It is thought that the accelerator and the inhibitor react or combine to form a reaction product or compound which does not promote the vulcanizing reaction of the vulcanizable composition (under the preliminary conditions such as mixing and milling) but which, under the vulcanizing conditions such as increased temperature, dissociates and liberates the accelerator which then acts in its accelerating capacity, and the inhibitor may re main inert or may itself act as an accelerator.

In other words, the critical temperature of the accelerator, with respect to its initiating prematurely the vulcanizing reaction in the rubber, is apparently raised to a point above the temperatures of milling or compounding and Within the range of the vulcanizing treatment.

The compounds manifesting such inhibiting action upon premature initiation of vulcanization by accelerators (and more especially the ultra accelerators and thosesometimes referred to as semi-ultra acceleratorsamong which may be mentioned the thiazoles, represented b mercapto benzo thiazole, certain disulphides such as tetra methyl thiuram disulphide, certain monosulphides such as tetra methyl thiuram monosulphide, etc., and their derivatives) are found to typically include the nitroso-amines which may be represented by the empirical formula in which R and R represent alkyl or aryl radicals (or nuclei) which may be alike or unlike and in turn may contain or be associated with one or more substituents.

Of the substituted nitroso-amines as thus defined, it is found that those compounds characterized by containing a naphthyl radical are particularly suitable as inhibiting compounds. For example, dialpha naphthyl nitroso-amine is typical of this group or class of compounds.

In a representative example of the invention, rubber and the usual vulcanizing and I .filler materials, together with the desired temperatures.

amounts of the accelerator compound and inhibiting compound, may be compounded and mixed in the usual manner as by milling (without premature vulcanization or scorching), and subsequently molded and vulcanized to the required degree of cure, by heating to the usual range of vulcanization The rate of vulcanization and degree of cure obtained may be accurately controlled by the time and temperature of vulcanization, to provide'a final cure equal to or better than that obtained without the use of the preliminary inhibiting compound or prehibitor.

In a preliminary scorching test, for example, in which the compounds were subjected to especially high temperatures during the mixing and milling operations until scorching was effected, a rubber composition containing:

100 parts rubber (smoked sheet) 3 parts sul hur 5 parts Zn A; part mercapto benzo thiazole 100 parts rubber (smoked sheet) 3 parts sulphur 5 parts ZnO .15 part tetra methyl thiuram disulphide .75 part dibeta naphthyl nitrosoamine produced scorching in about 72 minutes. Under like conditions the same compound,

without the dibeta naphthyl nitrosoaimine, was scorched in twenty minutes.

A third compound,- having the formula:

100 parts rubber (smoked sheet) 3 parts sul hur 5 parts Zn .15 part tetra methyl thiuram mono- I sulphide .75 part dibeta napththyl nitroso-amine was treated in the same way as the preceding compounds and scorching took place in 118 minutes, while the same compound, without dibeta naphthyl nitroso-amine, was scorched in about 65 minutes, under the same conditions.

This test, developed for the purpose, serves to measure the degree of the retarding or inhibiting effect of the inhibiting compound upon the vulcanization reaction and the accelerating influence of the ultra accelerator at temperatures of about 100 C. or less, as contrasted with vulcanizing temperatures which as ordinarily employed are above 120 C.

Similar tests were carried out employing the same composition, but with a dilierent lot of smoked sheet rubber which tended to scorch slower (Without the addition of prehibitor) than the rubber employed above. The results obtained are given below:

Table I s'rocx Rubber 100 Sulphur 3 Zinc oxide 5 Tetramethyl thiuram disulfide 0.15

Minutes before scorching Stock without prehibitor 44 With addition of 0.75 part of:,-

Diphenyl nitroso-amine 110 Dialpha naphthylnitros'o-amine 62 Phenyl beta naphthylnitroso-amine 93 Phenyl alpha naphthylnitrosoamine 93 Di-orthotolyl nitroso-amine 97 Phenyl orthotolyl nitroso-amine 102 Phenyl paratolyl nit-roso-amine 102 Benzyl phenyl nitroso-amine 52 Methyl phenyl nitroso-amine 57 Diethyl nitroso-amine 55 Piperidine nitroso-amine 55 Car-bazol nitroso-amine 46 In a typical application of the invention to the usual vulcanizing procedure, rubber compounds were prepared as follows:

100 parts rubber 40.5 parts carbon black 5.0 parts ZnO 3.0 parts sulphur 5.0 parts mineral rubber 3.0 parts stearic acid .8 part mercapto benzo thiazole Same as Formula I with addition of 1.0 part diphenyl nitroso-amine.

, III Same as Formula I with addition of .75 part diphenyl nitroso-amine.

Same as Formula I with addition of .50 part diphenyl nitroso-amine.-

: These were mixed by milling in the usual manner, care being taken, especially with the compound of Formula I, to prevent preliminary vulcanization or scorching. The mixed Om compounds were then la1d 1n thln sheets 1n e stock 3009 5007 tens11e elongaa vulcanlzmg mold and Vulcamzed at 20. lbs. per tion in Min Pounds sq. in. per cent pounds steam pressure. Samples of each pressure 5 compound were vulcamzed, for perlods of 4 I 4 2 1 r0 30, {15 and mlnutes, respectlvely. One A 3 9 8 2 p0rt1on of each sample Was then sub ected to g a tenslle strength test, the results belng glven 3 A 20 843 2250 g 3000 0 0 1n the followlng table. 75 20 880 2390 3m ('35 75 20 985 2000 l 4200 705 Table II 75 20 850 2280 i 3700 000 l 90 20 080 24001 3890 000 Cure at twenty pounds steam pressure g8 g3 1323 3938 l 5:

Mmutes 20 20 900 2580 3950 050 tlgineil final nsl e e onga- 300% 500% per tionin Table IV sq. in. per cent .4 B c D I A 735 1965 '3460 685 Smoked sheets 1'00 100 100 100 Carbon black... 40 40 40 40 II A 380 I140 2120 675 Mineral rubber. 5 5 5 5 Zinc oxide 5 5 5 5 III A 583 1075 2030 080 'S111phur 3 3 3 3 Stearic acid 3 3 3 3 IV .l A 637 1820 3100 665 Mercapto benzo thiazole 0.8 0.8 0.8 0.8 Dibeta naphthyl nitrosoamine..- 0 0.75 0 0 Phenyl beta naphthyl nitroso- 0 O 0 45 M amme 0 .75

m es Phenyl alpha naphthyl nitroso- Final Final 81311138 0 0 0 0. 75 tensile elonga- 300% 500% lbs. per tionint Sq-HL, per 0611 l 15 1 1 rma ens1 e e ongn- A 958 2420 4050 070 Stock M Pounds 300% 500% lbs. per 11011 int A moo 680 ll] p ss e sq. In. percen 60 Minutes 75 20 850 2200 3800 7 75 20 867 2360 3850 650 Fine] 01ml 75 20 000 2365 3840 005 300% 500% 2880551; 75 20 840 2320 3760 055 sq. in. per cent 90 20 940 2430 4000 075 0 38 33 332 Z383 2333 22 I! I A 1105 2830 4050 040 D 9o 20 970 2580 4000/ 655 III A 1135 2880 4175 035 Table V IV A 1120 2930 4220 025 A B C D Smoked sheets 100 100 100 100 S1m1lar vulcanlzlng experlments were carcarbon black", 40 40 40 40 rled out wlth composltlons contalnmg other fg g gfigg flff mtroso-amlnes, lncludmg both llke and ungt gpggga g g g llke substltuent groups, and hydrocarb n 1 0 10 5 00 1 011286152015. I (03.8 8.8 0.8'

ie yni roso-amine... 5 0 radlcals off both the a11phat1c and aromatlc Piperidine nimswmmen: 0 0 M5 n senes, as lndlcated 1n the above 11st 1n con- Methyl phenyl 1058001111110".-. 0 0 0 0.75 nect10n wlt-h the scorchmg test.

The experlmental results are presented 1n Final Final the followlng tables: tensile 610m.

Stock 300% 500% lbs Pounds pet t1on 111 Table III M111 pressure sq. 1n. per cent A B 0 D 00 20 075 1870 3350 000 00 20 715 1055 3475 075 00 20 820 2200 3780 ,000 .Smoked sheets 100 100 100 100 60 20 712 2020 3370 665 Carbon black... 40 40 40 40 Mineral rubber- 5 5 5 5' 75 20 780 2120 8550 080 Zinc 01005.. 5 5 5 5 75 20 805 2450 3860 055 Sulphun..- a 3 3 a 75 20 1055 2820 4220 040 Stearic 5510 3 s 3 a 75 20 000 2400 5040 055 Mercapto benzo thiazo 0. 8 0.8 0. 8 0.8 Phenyl beta napthyl nitroso- 90 20 922 2440 3970 (170 01111110 0 0. 75 0 0 90 20 982 2010 3910 040 Benzyl phenyl nitroso-amine 0 0 0.75 0 90 20 1168 2900 4160 630 Carbnzolnitroso-umine 0 0' 0 0.75 90 20 1120 2825 4120 680 Table VI A B O D Smoked sheets 100 100 100 100 Carbon black 40 40 40 40 Mineral rubber- 5 5 5 '5 Zinc oxide 5 5 5 5 Sulphur 3 3 3 3 Stearic acid 3 3 3 3 Mercapto benzo thiazole 0.8 0.8 0.8 0.8 Dialpha naphthyl nitroso-amine. 0 0. 75 0 0 Phenyl tolyl nitroso-amine 0 0 0.75 0 Ditolyl nitroso-amine i 0 0 0 0. 75

Cum Final Final- P d 300% 500% are 2 .22%: mm s q Min. pressure sq. in. per cent From the data thus obtained it is to be observed that, not only are the rubber compounds prepared with an addition of the diphenyl nitroso-amine, for example, free from the tendency toward preliminary vulcanization or scorching, but that when vulcanized at 20 pounds steam pressure and for the periods of time indicated, the vulcanized product exhibits as good or in some instances a superior cure (with respect to intermediate and final elongation values) than the co1nposition to which such addition has not been made.

It is therefore shown that by means of this inventionnot only may extremely active accelerators, (which have been hitherto un available for use in the rubber industry on account of their very high activity) be safely employed in rubber compounds and mixed and milled without initiating premature vulcanization, but the vulcanized rubber product is initially as good or better than rubber similarly compounded and vulcanized but without the addition of an inhibiting reagent.

It is also indicated that whereas diaryl substituted nitroso-amines are especially effective, with respect to the prevention of premature acceleration of vulcanization, the alkyl or dialkyl substituted nitroso-amines may also be used, although somewhat less effective.

Compounds which are in some respects related to the substituted nitroso-amincs above defined, and have been thus tested for use in accordance with the invention, include carbazole nitroso-amine which may be spoken of as mtroso N-carbazole,

N.NO

and in fact shows but little retarding effect in the scorching test. The piperidine nitrosoamine likewise does not manifest pronounced retarding effects. The results are given, however, because they are related to the other nitrose-amine compounds. Their failure to be more effective in these respects may be attributed to the valence linkage between the R and R groups of the nitroso-amine; which will be apparentfrom the formula of the former compound, as above given.

While the above disclosure relates to a preferred procedure, according to the invention, and to specific reagents employed in specific proportions, it is to be understood that variations may be made in both the mode of carrying out the invention and in the nature and amount of the several reagents used, according to the particular conditions of practice and the characteristics desired in the resulting product, as will be clearto those skilled in the art of treating rubber.

This application is a continuation in part of my application, Serial No. 323,556, filed- December 3, 1928, and is designated as Case III3 of a group of continuation applications filed on even date herewith.

I claim:

1. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an organic accelerator characterized by controlling the action of the accelerator with a dinaphthyl nitroso-amine.

2. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an organic accelerator characterized by controlling the action of the accelerator with dialpha naphthyl nitroso-amine.

9 3. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and a sulphur-containing organic accelerator characterized by controlling the action of the accelerator with a dinaphthyl nitroso-amine.

4. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and a sulphur-containing organic accelerator characterized by controlling the action of the accelerator with dialpha naphthyl nitrosoamine.

5. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an accelerator containing a thiazole nucleus characterized by controlling the action of the accelerator with a dinaphthyl nitroso-amine.

6. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and an accelerator containing a thiazole nucleus characterized by controlling the action of the accelerator with dialpha naphthyl nitrosoamme.

.7 Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and mercapto benzo thiazole characterized by controlling the action of the accelerator with a dinaphthyl nitroso-amine.

8. Method of vulcanizing rubber or rubber compositions with a vulcanizing agent and mercapto benzo thiazole characterized by controlling the action of the accelerator with dialpha naphthyl nitroso-amine.

9. An accelerator composition comprising an organic accelerator and a dinaphthyl nitroso-amine.

10. An accelerator composition comprising an organic accelerator and dialpha naphthyl nitroso-amine.

11. An accelerator composition comprising a sulphur-containing organic accelerator and a dina hthyl nitroso-amine;

12. Zn accelerator composition comprising a sulphur-containing organic accelerator anddialpha naphthyl nitroso-amine. v

13. An accelerator composition comprising an accelerator containing a thiazole nucleus and a dinaphthyl nitroso-amine.

1 1. An accelerator composition comprising an accelerator containing a thiazole nucleus and dialpha naphthyl nitroso-amine.

15. An accelerator composition comprising mercapto benzo thiazole and a dinaphthy nitroso-amine.

16. An accelerator composition comprising mercapto benzo thiazole and dialpha naphthyl nitroso-amine.

Signed by me at Boston, Massachusetts, this 1st day of June 1929.

- HENRY'B. MORSE. 

